The goal of this proposal is to develop a prototype intraoperative gamma-ray camera (IOGC) specifically designed for use in imaging gamma- emitting radiopharmaceuticals (such as 99m-Tc labeled Sestamibi) incorporated into brain tumors in the intraoperative surgical environment. The patient is injected with a tumor seeking radiopharmaceutical before surgery, the surgical procedure to remove the tumor mass is performed, and the site is then imaged using the IOGC probe to locate residual subclinical tumor cells. The proposed system is intended to improve the success of tumor removal surgeries by allowing more complete removal of subclinical tumor cells without removal of excessive normal tissue. The intraoperative gamma-ray camera will use a small and lightweight detachable head comprising a 256-pixel mercuric iodide (HgI2 detector array. During the Phase I feasibility study prototypical 19-element arrays were designed, built and characterized. The performance of the devices in terms of energy resolution, spatial resolution and uniformity proved the feasibility of the chosen approach, and exceeded the initial specifications. In Phase II a complete intraoperative imaging system including a 256-pixel imaging probe, processing electronics, and data collection hardware and software will be designed and developed. In the first year several detector arrays will be designed, built, fabricated, and evaluated at various levels in a specialized test chamber using brain tumor phantoms filled with medical radioisotopes. In the second year the probe and associated imaging system electronics and software will be completed, integrated and evaluated. The probe construction will be optimized for operation proximal to the tissue of the patient in, the surgical field in order to give the best sensitivity, spatial resolution, and contrast. PROPOSED COMMERCIAL APPLICATION: This proposal is motivated by the need for commercial intraoperative imaging cameras to improve the success of tumor removal surgeries. The proposed work is focused on a novel system to be constructed for patients with brain tumors. In addition, part of the proposed work will be to show that the design of the gamma- ray camera can be extended to accommodate various geometries, numbers of pixels, and specifications that will apply to additional clinical and commercial interests such as the identification of breast tumors in dense breast and assessment of malignancy in lesions identified as suspicious in mammography.